Water productivity as influenced by commodity prices and
irrigation systems
Results comparing the beneficial water use fraction (BWUF) and
physical and economic water productivity (WP and EWP) for all
treatments and irrigation systems as well as for both field sizes of
5 and 32 ha and commodity prices of 154 and 264 D t−1 are presented in Table 9. Results show that drip systems lead to higher
BWUF than set sprinkler and center-pivot systems. This is due to
lowersoilevaporationsincethewettedfractionofthesoilis fw = 0.6,
less than for sprinkler irrigation, where all area is wetted; therefore,
soil evaporation is less for drip than for sprinkling. Adopting Treatments A and C lead to higher BWUF than Treatments B and D for
all irrigation systems and all cases analyzed. Since BWUF is herein
defined as the ratio of ET
adj to TWU, that situation is due to the fact
that ET
adj is smaller for B and D, thus decreasing that ratio. Treatment B presents the lowest BWUF among all cases analyzed, which
results from the decrease of ET
adj caused by the stress imposed during the vegetative stage. Comparing the small and the larger field,
BWUF are similar for drip and set sprinkler systems but are smaller
for the center-pivot systems in case of the 5 ha field comparatively
to the 32 ha field.
When adopting full irrigation (Treatment A) a higher WP than
for other treatments is generally obtained. Similar results are
obtained for the C treatment, where stress is induced only during the late season. Because BWUF is also high for both treatments,
yield losses are null or minimized. For B and D treatments TWU
also decreases but proportionally less than for C, thus resulting in
lower WP. The highest values for WP correspond to the non stressed
Treatment A, varying between 2.60 and 2.80 kg m−3 for all systems
and management conditions. The lower WP values are obtained
for Treatment D under drip irrigation and Treatment C for centerpivot. This occurs because the water savings that are attained with
the stress imposed during the different crop stages are not enough